KB.15.15

9 QinQ (Provider bridging)

NOTE: All commands previously in the Summary of commands table are indexed under the entry

Command syntax.

Introduction

This chapter describes how to enable QinQ operations on the switch and how to configure provider

bridge S-VLANs and port assignments.

The IEEE 802.1ad specification, commonly known as QinQ or provider bridging, extends the IEEE

802.1Q standard by providing for a second tier of VLANs in a bridged network. The general

purpose of QinQ is to allow frames from multiple customers to be forwarded (or tunneled) through

another topology (provider network) using service VLANs or S-VLANs. The provider bridge, which

may comprise multiple devices in the service provider domain, looks like a simple bridge port to

the customer's traffic and maintains the customer's VLANs.

Figure 74 (page 322) shows a sample QinQ topology and use model. Customer A has LANs spread

across multiple site locations and may want to link them together in a single logical LAN. To do

this, the customer could have a cable laid out for the entire distance interconnecting the three sites.

A more cost-effective and scalable alternative, however, would be to tunnel frames through the

provider's network to interconnect all the sites subscribing to the service. This solution can be

delivered using QinQ.

Figure 74 QinQ network diagram

The Service Provider and customers may belong to the same business entity, as in the case where

a single enterprise uses QinQ to help segregate local networks and increase the scalability of their

backbone infrastructure.

How QinQ works

Under QinQ, the provider network operates on a different VLAN space, independent of the VLANs

that are used in the customer network.

322 QinQ (Provider bridging)